There are two methods to upgrade the R4iDSN 3DS card / R4iDSN non 3DS card to work on DSi V1.4.2 ,

This patch is designed for r4idsn 3ds / R4idsn non-3DS version card released by r4idsn.com.
In order to make your r4idsn card run on NDSi V1.4.2, you should update your r4idsn with this patch.
Please do as the procedures listed below.

(1)The procedures for V142_Patch_NDSL.nds
1.Download the latest WOOD R4 for R4iDSN from www.r4idsn.com and unzip it to the root directory of your tf card
2.Copy V142_Patch_NDSL.nds to your tf card
3.You should get a NDSL

4.Just power your NDSL on and boot up V142_Patch_NDSL.nds
5.Take your R4iDSN out of the NDSL
6.Reinsert your R4iDSN into the NDSL
7.Press KEY_A and the updating process will begin
8.You should keep your NDSL powered on during the updating process
9.IF the result shows SUCCESS, it means you have updated your R4iDSN with success and this card can work on NDSi V1.4.2

For the users whose r4idsn has been broken, you can get a NDSL and another flashcard.
Just boot up V142_Patch_NDSL.nds with the other flashcard and reinsert your R4iDSN.
You can also update your R4iDSN.

(2)The procedures for V142_Patch_NDSi.nds

1.Download the latest WOOD R4 for R4iDSN from www.r4idsn.com and unzip it to the root directory of your tf card
2.Copy V142_Patch_NDSi.nds to your tf card
3.You should get a NDSi
4.Just power your NDSi on and boot up V142_Patch_NDSi.nds
5.Attention:do not take out your R4iDSN
6.Press KEY_A and the updating process will begin
7.You should keep your NDSL powered on during the updating process
8.IF the result shows SUCCESS, it means you have updated your R4iDSN with success and this card can work on NDSi V1.4.2

Source:http://www.coolgadgetsgift.com/how-to-get-r4idsn-card-to-work-on-v1.4.2-firmware-dsi-en.html